The invention is directed to a process for the recovery of 3-cyanopyridine from the gaseous mixture resulting from the catalytic reaction of 3-methylpyridine with ammonia and oxygen.
There are known numerous processes for the production of 3-cyanopyridine by the catalytic reaction of 3-methylpyridine with ammonia and oxygen in the gas phase. These processes differ essentially in the catalysts used. For example, there can be employed as catalysts tin vanadate in admixture with phosphorus pentoxide on aluminum oxide, silica gel or their mixture (Japan published application No. 42-6066) or molybdenum oxide in admixture with oxides of vanadium, chromium, manganese or cobalt on aluminum oxide, magnesium oxide, silica or titanium dioxide (Japan published application No. 45-13572) or pure vanadium pentoxide of specific surface area and particle size (German OS No. 2435344). Especially suited are catalysts which are produced by pretreating by heating to temperatures of 600.degree. to 1100.degree. C. in the presence of oxygen mixtures which contain at least one of the elements titanium, iron, copper, cobalt, manganese and nickel and in a given case, a carrier (German Pat. No. 2039497 and related Lussling U.S. Pat. No. 3,927,007). The entire disclosure of the Lussling U.S. patent is hereby incorporated by reference and relied upon.
The gaseous mixtures formed in the catalytic reaction generally contain, independent of which catalyst is used, 3-cyanopyridine, ammonia, in a given case, unreacted 3-methylpyridine and byproducts such as water, carbon dioxide, nicotinamide, and hydrogen cyanide. The working up is essentially directed to obtaining the 3-cyanopyridine as well as the recovery of excess ammonia and the unreacted 3-methylpyridine. In order that the ammonia can be returned to the cycle and used again, it is necessary to separate it from carbon dioxide and the remaining byproducts.
In a known process for the production of 3-cyanopyridine by catalytic rreaction of 3-methylpyridine the reaction mixture is cooled with dry ice, the part condensed thereby is washed with a solvent such as benzene, and the 3-cyanopyridine and the 3-methylpyridine present, in a given case, recovered from this solution by distillation (U.S. Pat. No. 2,861,999). In another process the reaction mixture is washed with water, the aqueous solution extracted with ether, and the 3-cyanopyridine recovered by distillation off of the ether (Great Britain Pat. No. 777,746. In regard to the recovery of the excess ammonia, it occurs in both cases as an aqueous solution, nothing is said. The recovery is expensive and might not be without considerable loss.
In further process the reaction mixture is washed with methanol at low temperature and in this manner the 3-cyanopyridine, in a given case the 3-methylpyridine present, and some ammonia separated (German OS No. 2,435,344). In this process the main portion of the ammonia remains in the residual gas. However, it is disadvantageous that this also contains byproducts, such as especially carbon dioxide, which are enriched and disturb the reaction if the residual gas is repeatedly recirculated.